Tap-to-Pay with Tangem

How it works

1. Merchant enters the amount on NectarPOS and shows "Tap to pay".
2. Customer taps their Tangem card on the back of the terminal. The POS reads the card's public key over NFC.
3. Nectar.Pay builds the USDC transfer transaction and sends the 32-byte digest back to the card.
4. The Tangem card's secure element (EAL6+) signs the digest inside the chip. The private key never leaves the card.
5. Nectar.Pay assembles the signed transaction and broadcasts it to Ethereum. Merchant sees a check mark. Done.

What customers need

• A Tangem card (any 2.0+ card, single or backup set), activated via the official Tangem app.
• USDC on Ethereum mainnet loaded to the card's ETH address.
• A small ETH balance (~$2 worth) for network gas. NectarPOS shows a clear error if the card can't cover gas.

What merchants need

• A NectarPOS Android terminal (v0.1.4+ — the version that ships with the Tangem NFC plugin).
• A USDC (Ethereum) payout address configured on your store. Set it at Store → Chains → USDC (Ethereum).

Security model

• Signing keys live in the Tangem card's certified secure element. Nectar.Pay never touches them.
• Each tap creates a single-use payment intent with a 60-second TTL. Once broadcast, the intent is retired.
• Server-side ecrecover verifies the signature matches the card's address before broadcast. A wrong or tampered signature is rejected.
• The on-chain nonce is fetched at build time — replaying the same signed tx after confirmation fails at the mempool.

Fees

Nectar.Pay charges no per-tap fee for Tangem payments during the initial rollout. Customers pay Ethereum network gas (typically $0.30 – $2 depending on network conditions). Merchants receive the full USDC amount at their payout address.

Coming soon

• USDC on Base and Arbitrum (gas well under $0.05).
• Tangem cards with an access code / PIN for high-value taps.
• Merchant-side refunds via a store treasury Tangem card.